The Settings>Sounds option is there. It just doesn't work. In the first 6 months of owning the Droid 2, this never happened.
Someone mentioned Sound Manager above. Is that an app or a Settings feature?

Don't know what phone/system you have, but there is no "battery notification" option on the stock Samsung Charge (at least not under Settings> Sound Settings). However, I have noticed that if you go to Sound Settings, you can silence the "Notifications." This will obviously silence all your other notifications too, but the ringer will still be available.